Greenhouses constructed of PVC offer an inexpensive alternative to glass or prefabricated greenhouses. In temperate regions, a greenhouse can greatly extend the growing season, allowing a gardener to start seedlings early and continue to harvest later in the season. A PVC greenhouse warms the air temperature considerably and prevents damage from frost, dew, and heavy rains and even hinders many insects that might attack plants. Most PVC greenhouses come with pre-formed joints for easy assembly. However, if the pieces don't fit together because of burrs or rough edges, a handheld rotary tool with a grinding stone or sanding band accessory will smooth these areas out for a perfect fit.
Greenhouses made from PVC utilize a variety of roof styles, ranging from simple to complex. The simplest, "hoophouse" roof style consists of a series of PVC arches. More complex roof styles include "A" frame and Gothic arch designs. The typical "A" frame greenhouse uses a PVC ridge line element to stabilize and connect slightly arched PVC ribs on either side. The Gothic arch design includes additional horizontal PVC elements to form walls, which are connected to the ridge line by PVC rafters.
Covers for greenhouses made of PVC typically consist of UV-resistant polyethylene plastic sheeting stretched over the PVC frame. The thickness of the plastic usually ranges from 4 to 5 mil, but may vary based on the local climate and the budget of the gardener. In extremely sunny regions, PVC greenhouses may require an additional shade cloth covering over the top of the plastic sheeting; this is usually a removable cover secured by ropes and ground stakes. In some areas where PVC greenhouses are used to provide protection from insects or prevent unwanted cross-pollination, the cover may consist entirely of netting or screenwire. Sections of cut black poly pipe, binder clips or special "snap clamps" secure the plastic sheeting or netting to the PVC frame.
Greenhouses made of PVC require sturdy anchoring, because they are very lightweight and could easily catch the wind and blow away. Basic hoophouse designs use metal rebar or heavy-duty plastic stakes hammered into the ground on either side of the frame to anchor the arches; the arch pipes slide onto the anchors and use tension to lock into place. More complex designs involve a PVC base frame anchored to the ground with stakes or a heavy, wooden base frame which holds the structure in place.
Greenhouses made of PVC vary greatly in durability and permanence. Temporary PVC greenhouses usually lack end frames; the ends may remain open or may be covered with flaps of plastic. More permanent PVC greenhouses often consist of a wooden base for securing PVC ribs and wooden end frames with doors; rigid, corrugated plastic often covers the end frames, whereas plastic sheeting covers the top of the structure. Intermediate designs involve PVC end frames with doors and walls covered with plastic sheeting.
Greenhouses made of PVC, like all greenhouses, require a substrate that drains easily and hinders weed growth. However, the surrounding ground must remain intact in order to secure anchors and ground stakes. As a result, many gardeners choose to simply add a layer of sand covered with a layer of gravel to the interior of the PVC greenhouse after construction.
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